Arteries and veins may locally, abnormally flutter and form arteriovenous aneurysms due to injury, vascular sclerosis, high blood pressure, bacterial infection, disorder of venous valves, malformation, etc. Among these arteriovenous aneurysms, those which have bosselated walls of intracranial arteries such as internal carotid arteries, anterior cerebral/anterior communicating arteries, middle cerebral arteries, and vertebral basilar arteries are called cerebral aneurysm that induces subarachnoid hemorrhage when ruptured. It is said that about 10% of stroke is subarachnoid hemorrhage and reported that the appearance of patients with the disease is as many as 30,000 a year in Japan. It is also said that 80% or more of such patients will usually die after repeating the rupture of cerebral aneurism. Therefore, both the finding of cerebral aneurism at an earlier stage and the embolization of affected parts must be the best way to prevent subarachnoid hemorrhage.
As conventional methods for embolizing cerebral aneurysm, direct surgeries such as clipping and ligation of parent arteries of aneurysm have been generally used, but they have been frequently replaced with intravascular surgeries that embolize cerebral aneurysm by inserting platinum coils into the cavity of cerebral aneurysm in these days. However, the method using platinum coils has the drawbacks that the installation of materials such as blebs with a complicated shape might possibly fail the complete embolization of aneurysm, the installed coil might cause recirculation of blood when compressed within the aneurysm, and that thrombus formed interstitially in the aneurysm might move into a normal brain part to cause fatal cerebral infarction.
As a method of overcoming the above drawbacks of conventional methods, the present inventors proposed in Japanese Patent Kokai No. 107,549/94, etc., a liquid embolizing material for embolizing aneurysm which is used for embolization in such a manner of injecting into the cavity of aneurysm a non-water-soluble macromolecule such as cellulose acetate dissolved in a water-soluble organic solvent, dispersing the water-soluble organic solvent throughout the cavity, and precipitating and solidifying the macromolecule therein to embolize the aneurysm. Since the above embolizing material also exerts a remarkable effect on aneurysm having a complicated shape of cavity, it has been valued as a theoretically advantageous one. The macromolecule used, for example, in Japanese Patent Kokai No. 107,549/94, however, there still remains a problem to be solved in preparing a relatively high quality, stabilized embolizing agent in a satisfactorily yield because the macromolecule has inconsistent solubility and viscosity in water-soluble organic solvents such as dimethylsulfoxide (may be abbreviated as “DMSO”, hereinafter).